やばい(yabai) means: dangerous; risky; awful; terrible; crap; terrific; amazing; cool
The positive meaning of the word is recent though that's mostly referred to these days - though of course it all depends on context.
Adding the そう(sou) to the word, makes it mean like "It seems like it's going to be [yabai]." So what he says is "it seems like it's going to be amazing."